LanguageTool is a style and grammar checker that
currently supports English, Polish, German, French, Dutch, and other languages to a different degree. It scans the words and their part-of-speech tags for occurrences of error patterns, which are defined in an XML file. More powerful error rules can be written in Java.

RTextDoc is a text editor with proofreading.
It is designed for typesetting professional research papers and manuals using the LaTeX, AsciiDoc, and DocBook
markup languages. It includes on-the-fly spelling and grammar checking, syntax highlighting, bracket matching, folding, a document structure browser for sections and labels, bookmarks, a manager for LaTeX symbols, WYSIWYG equation editor, and integrated BibTex database manager.

After the Deadline for OpenOffice.org is a smart English grammar, style, and contextual spelling checker for OpenOffice.org. The grammar checker highlights common errors in your writing. The style checker (off by default) finds passive voice, clichés, redundant phrases, and complex expressions. The contextual spelling checker looks for misused words and reports them to you. This extension communicates with an open source software service to check your writing. You may run your own server or use that provided by afterthedeadline.com. Text sent to afterthedeadline.com is sent over SSL and none of it is kept.

Kouprey is a library that can be used to build and run parsers based on the Parsing Expression Grammar (PEG) formalism. It does not have any special requirements beyond standard ECMAScript/JavaScript, and can be used to parse arbitrarily complex languages inside a Web browser or other JavaScript runtime. It has been used to parse complex general purpose programming languages, and comes with numerous examples.

XML-Grammar-Fiction is a Perl package that provides processors for lightweight markup languages and corresponding XML grammars for writing prose (e.g. stories, novels, and novellas) as well as screenplays. The XML grammars can in turn be translated to XHTML and DocBook/XML. XML-Grammar-Fiction currently offers only very basic functionality, but has good support for UTF-8 and allows one to write bidirectional texts conveniently. It is still under development and may exhibit some quirks.

UniCC, (Universal Compiler-Compiler) is a powerful LALR(1) parser generator and language development system for computer professionals. It serves as an all-round design and build tool assisting compiler writers in any parsing-related task, including production quality compiler construction and the implementation of domain specific languages. It unifies an integrated generator for lexical analyzers and a powerful LALR(1) parser generator into one software solution.
The programming interface is a rich, extendable, and innovative BNF-based grammar definition language for expressing context-free grammars.

Voca is a vocabulary trainer for foreign languages. It allows you to create and manage your own word lists and share them online. You can make word lists for any language or for other things you want to memorize. It lets you do different types of exercises, including grammar, pronunciation, and picture tests. It lets you take tests with open answers, self-check, or multiple choice. Voca has support for multiple translations of a single word.

The Parsing Expression Grammar Template Library (PEGTL) is a C++0x library for creating parsers according to a Parsing Expression Grammar (PEG). Grammars are embedded as regular C++ code, created with template programming (not template meta programming). These hierarchies naturally correspond to the inductive definition of PEGs. The library extends on the subject of PEGs with new expression types, actions that can be attached to grammar rules, and mechanisms to ensure helpful diagnostics in case of parsing errors. PEGs are superficially similar to Context-Free Grammars (CFGs).